Means for the quantitative analysis of deuterium in hydrogen-containing compounds



3,066,220 EUTERIUM IN Nov. 27, 1962 G. NIEF ETAL MEANS FOR THE QUANTITATIVE ANALYSIS OF 1) HYDROGEN-CONTAINING COMPOUNDS 2 Sheets-Sheet 1 Filed Aug. 27, 1959 Nov. 27, 1962 G. NIEF ETAL 3,066,220

MEANS FOR THE QUANTITATIVE ANALYSIS OF DEUTERIUM IN HYDROGEN-CONTAINING COMPOUNDS Filed Aug. 2", 1959 2 Sheets-Sheet 2 FIG.4

rates atent Office 3,066,226 Patented Nov. 27, 1962 3,066,220 MEANS FOR THE QUANTITATIVE ANALYSIS or nEtJrEruUM IN HYDROGEN-CONTAINING COMPOUNDS Guy Nief, Paris, and Ren Batter, Chatillon-sous-Bagneux, Seine, France, assignors to Commissariat a lEnergie Atomique, Paris, France Filed Aug. 27, 1959, Ser. No. 836,529 Claims priority, appiication France Aug. 30, 1958 4 Claims. (Cl. 25041.9)

The invention relates to improvements in means for the quantitative analysis of deuterium in hydrogen-containing compounds.

As is well known the respective components of a gaseous mixture of hydrogen and deuterium can be quantitatively estimated by means of a mass spectrometer. However, if it is desired to carry out a quantitative analysis of the deuterium in hydrogen-containing compounds, as for example in light water, H O (as opposed to heavy water, D it is advantageous to reduce such compounds in order to cause their hydrogen and deuterium to appear in the free gaseous state. Where this operation is effected, it is very difiicult to prevent the reduction thus carried out from having a quantitatively distorting action on the reduction products; that is to say to ensure that the proportions of hydrogen and deuterium obtained after reduction, and intended to be ionised and introduced into the mass spectrometer, are really the same as the proportions actually present in the compounds under investigation. Moreover, it is very important that the reduction should be effected rapidly, so that the consecutive quantitative analyses can be carried out rapidly in the mass spectrometer with suflicient accuracy to make the results obtained worthwhile despite the small proportion of deuterium with respect to hydrogen in the usual run of hydrogen-containing compounds.

A principal object of the present invention is the provision of means for quantitatively analysing deuterium in hydrogen-containing compounds which overcome the disadvantages described above and enable a high degree of accuracy to be obtained.

This invention consists broadly in quantitatively analysing the deuterium contained in hydrogen-containing compounds, by means of a mass spectrometer which separates ions having an atomic mass of two (i.e. that of a hydrogen molecule) from ions having an atomic mass of three (i.e. that of a molecule consisting of a hydrogen atom and a deuterium atom), the said hydrogen-containing compounds being reduced in a device known as a gas line located before the mass spectrometer and in which the actual reduction takes place in a uranium reduction oven disposed between the leak via which gas is introduced intothe spectrometer and the spectrometer itself.

In preferred embodiments of this basic apparatus, it is provided with one or more of the following additional features:

(a) The uranium in the reduction oven is in the form of one or more tapes or the like, of, for example, between 4 and 24 cms. long, between 1 and mms. wide, and very thin, preferably between 0.1 and 0.4 mm. thick, the said uranium being heated to a temperature of the order of 600 C.;

(b) In the gas line, the gases pass through two capillary tubes, situated respectively on either side of the uranium reduction oven; and

(c) The strip or strips of reducing uranium are disposed in a U-shaped silica tube, while the remainder of the gas line preferably consists of a glass based on aluminium borosilicate and sodium, such as that commercially available under the name Pyrex.

In addition to the above-described basic apparatus and the above-described preferred features thereof, the invention further comprises additional arrangements which are preferably used at the same time. They are apparent from the detailed description which follows, but the following among them will be particularly mentioned:

(a) An arrangement in which vacuum is set up in the tube of the mass spectrometer with the aid of three pumps in series, i.e. a conventional primary pump and two mercury-diifusion secondary pumps whereof at least one comprises an ejector;

(b) An arrangement in which the two ion currents emanating from the mass spectrometer are separately amplified before their ratio is measured; and

(0) An arrangement in which the absolute value of the proportion of deuterium in the hydrogen-containing compound being analysed (for example: a specific water), is determined to a satisfactory approximation by relating the numerical results of at least two measurements made on the said water using at least some of the arrangements according to the invention, to the values of two substantially linear curves which express the quantitative analysis of deuterium, in the liquid and vapour phase respectively, in a mixture of hydrogen sulphide and reference waters containing a specific mixture of pure light water and pure heavy water.

In order that the invention may be more fully understood, certain preferred embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which FIGURE 1 is a diagrammatic overall view of apparatus for carrying out quantitative analysis by means of a mass spectrometer;

FIGURE 2 is a diagrammatic view of the gas line forming a part of the apparatus illustrated in FIGURE 1;

FIGURE 3 is an electrical circuit diagram of an arrangement incorporating the present invention adapted to give expression to the analysis carried out by the spectrometer; and

FIGURE 4 is a graph illustrating another arrangement according to the invention adapted to make still more advantageous use of the results given by a mass-spectrometer analysing apparatus according to the invention.

FIGURE 1 shows a tube 1 of a mass spectrometer and details of the device for pumping out the tube 1, said device being connected to the tube 1 of the spectrometer by a pipe 4a. The gas line itself is included in a rectangle gas line which conveys the gases which are to be analysed to the tube 1, a primary pump 4, which sets up the desired vacuum in said gas line, is connected thereto by a pipe 4a. The gas line itself is included in a rectangle outlined at 5; its construction which comprises the use of a plurality of the features of the invention, is shown in detail in FIGURE 2.

The mass spectrometer used is a modification of a conventional spectrometer in which the tube 1 is curved through 60 (in technical language, such a spectrometer is said to have a 60 magnetic prism), with a mean radius of curvature of 5 cms., at the bend 6. The spectrometer also comprises a source of ions 7, a source magnet 8 which focusses the ions in the source, slots 9 related to the side of the source, a main magnet 10 which imparts different deflections to the two ion beams produced, an electrical collector 11 for H? ions of mass 2, and a collector 12 for HD+ ions of mass 3; the spectrometer in question is therefore a mass spectrometer of the two-three type.

Independently of the gas line and its particular reduc tion device, a certain number of particular arrangements have been developed for such a spectrometer; these arrangernents form part of the invention and contribute to the quality of the results which the invention makes it possible to obtain. These arrangements are briefly est tes described hereinafter without enlarging on explanations of the corresponding detail which will be well known to those skilled in the art.

In one of these arrangements, the tube 1 is pumped out by means of three pumps in series, i.e. a primary pump 13, which is generally of the vane type, and two mercuryditfusion secondary pumps 14 and 15. The pump 14 is equipped with an ejector. It is strongly heated, and provides primary vacuum for the pump 15, which has a nominal delivery of 30 litres per second.

Being given that, for pumping hydrogen as is the case here, the pumping rate depends especially on the power with which the pumps are heated (and moreover that it depends thereon in a different manner for the respective molecules of H and HD, which could have unfavourable repercussions on the accuracy of measurements being carried out), it is advantageous to provide, between the pump 15 and a solid carbon dioxide trap 16, a constriction which limits the undesirable effects due to this phenomenon, and also retards distillation of mercury from the pumps towards the trap 16. A gauge 17 of known type and various traps and safety devices illustrated at 18 and 19 complete the pumping unit.

The various pumping arrangements described enable pumping to be kept up for more than six months without interruption, the device according to the invention meanwhile remaining highly eflicient and strictly accurate in operation, without the heating of the pumps having any effect on the measurements obtained.

Another particular arrangement relevant to the spectrometer concerns the source of ions for the latter. In order to obtain large ion fluxes, a filament emission current of 4 milliamperes is used, while the output slot 9 is 1.5 mm. wire; this produces a strong electric field, of approximately 50 v./cm., in the ionisation chamber of the tube 1, and, in particular, almost completely prevents the formation of H? ions, which would be undesirable since in this case measurements are only carried out on H and I-ID ions.

Another arrangement concerns the receiving slots which are one of the elements of the collector members 11 and 12 for each of the two ion beams and which enable the strength of the said beams to be measured. In order to facilitate adjustment, these slots are made relatively wide (for example 0.5 mm.). Moreover, the planes of the two slots are respectively disposed perpendicularly to the mean axis of each of the two electron beams and, at least sub- Ztantially, at the focal points of the corresponding ion eam.

The mass spectrometer and the collectors enable the ion currents to be measured, preferably by means of an electrical circuit as shown in FIGURE 3, which will be described later. It is nevertheless important for the gaseous currents of H and HD reaching the spectrometer via the tube 3 (FIGURE 1) to have a quantitative compipe 3 which provides a connection to the mass spectrometer, comprises the following principal integers: a liquid 'nitrogen tra'p 21 of known type; four taps 22a, 22b, 22c,

22d; an expansion bulb 23; and a uranium reduction oven 24.

The tap 22a serves to isolate the gas line from the vacuum-pumping device 4. The tap 22b enables an inlet 25 to be placed in communication with the expansion bulb 23, while the inlet 25 enables a sample of any particular liquid hydrogen-containing compound (this will often 'the gas introduced into the oven.

be water) whose deuterium content is to be measured, to be introduced. The tap 22c enables a gaseous hydrogen-containing compound, such for example as hydrogen sulphide, to be directly introduced; for this purpose it comprises a ground inlet 26 which can be fitted to a container filled with the gas to be investigated.

The uranium reduction oven 24 is disposed, as stated above, between the leak 27 through which the hydrogencontaining gas in introduced into the spectrometer and the spectrometer itself.

The uranium contained in the oven 24 is in the form of two very thin tapes 28a and 28b, each disposed in one branch of a U-shaped tube 29 which is preferably made of silica. Each of the two uranium tapes has the following dimensions, length: 8 cms.; width: 2.5 mm., thickness: 0.2 mm. The advantage of using such a very thin sheet of uranitun is that the time taken for the gas to become diffused in the metal, which is proportional to the square of the thickness of the latter, is reduced. Reaction equilibrium, corresponding to saturation of the metal, is thus reached in a very short time under the above conditionsapproximately a minute.

The advantage arising from the particular location of the uranium reduction oven follows from the considerations specified below:

It is known that uranium heated to a temperature of approximately 500 C. quantitatively reduces certain hydrogen compounds, such as water, hydrogen sulphide and ammonia, to hydrogen. At this temperature, however, the solubility of hydrogen and that of deuterium in uranium are governed by different laws, and this difference in solubility could constitute a serious source of error in a device similar to that of the present invention if special measures were not taken to nullify it. However, if the reduction pressure is greater than the pressure in the ion source of the spectrometer tube 1, the gas produced by reduction tends to flow on its own towards the spectrometer tube without any need for it to be recompressed. Moreover, since total reduction is effected in the gas line, the hydrogen which passes out of the oven when the reducing uranium is saturated with dissolved gas has the same isotope composition as Nevertheless, the quantity of uranium metal is preferably limited to that present in tapes having dimensions of the order indicated above since the quantity of hydrogen-containing compound to be reduced is only that which gives rise to the hydrogen which must, in fact, be introduced into the ion source of the spectrometer tube. In addition, the pressure of hydrogen on the metal is very low, and the time taken for the uranium to become saturated is consequently short, which acts in the same sense as the fact, indicated above, that the metal is very thin.

The gas line illustrated in FIGURE 2 also incorporates a further preferred feature of the invention, namely the provision of a capilliary tube on each side of the oven 24. ()ne capillary tube 27, constitutes the leak through which the gas to be reduced is introduced into the oven. Suitable dimensions for the tube 27 are 10 cms. long and an internal diameter of 0.2 mm. The other capillary tube 30, which is disposed between the reduction oven 24 and the spectrometer tube, is 5 cms. long and has an internal diameter of 0.1 mm.

Introduction of the hydrogen-containing compounds to be analysed into the gas line is effected, in the case of liquids (water being the most commonly analysed liquid), through the inlet 25 and, in the case of gases, through the inlet 26.

If a liquid, for example water, is being dealt with, it is introduced with the aid of a small helix 31 of platinum wire mounted on a polyvinyl plug 32. Platinum is chosen because it is readily wetted by water and because it resists corrosion; moreover, it is very simply cleaned by heating the wire to red heat.

The following procedure is followed for introducing the water (or other liquid) into the gas line: the plug 32 is attached to the inlet 25, and the taps 22b and 22d are opened, while the tap. 22a and 220 are closed. Opening of the tap 22d causes the Water held by the small helix 32 to vaporise in the expansion bulb 23; the latter advantageously has a volume of 250 cubic centimetres. The small quantity of air (approximately 0.05 cubic centimetre) between the plug 32 and the tap 22d is, of course, simultaneously introduced into the bulb 23, but this does not involve any disadvantage, since air combines with uranium at 600 C. to give oxides and nitrides. The water vapour diffused through the capillary tube 27 then passes into the oven 24, Where it is reduced to hydrogen which then passes on to the ion source of the spectrometer.

Two further details of the improved gas line illustrated in FIGURE 2 are as follows: one is that it is advantageously constructed, before the U-shaped tube 29, of a glass based on aluminum borosilicate and sodium, for example that known by the trade name Pyrex; the other is that the taps are advantageously heated to approximately 85 C. in order to prevent water from being absorbed on the walls (the taps are therefore preferably lubricated with a silicone grease), while the other parts of the line are heated to approximately 160 C.; such heating is conveniently effected with electric heater wires E-E.

The apparatus illustrated in FIGURES l and 2 is employed in conjunction with a device for measuring ion currents, the latter device preferably incorporating one or more of the features of the electrical circuit diagram illustrated in FIGURE 3.

In the arrangement illustrated in FIGURE 3, the two ion currents produced by the source 7 in the tube 1 (which is illustrated here in a conventional simplified form), having been deflected in the tube as described above with reference to FIGURE 1, are respectively received by the collector member 11 in the case of H ions of molecular mass two and by the collector member 12 in the case of HD+ ions of molecular mass three.

The ion currents received by these collectors are respectively fed by connections 33a and 34a to amplifiers 33 and 34 via pre-amplifiers 33b and 34b respectively; the ratio of the output currents of the amplifiers 33 and 34 is measured by a decade box 35a, 35b and a galvanometer 36. If R is the ratio thus measured, the concentration C of deuterium with respect to H is expressed by a mathematical function of R and the output voltage V of the amplifier 33 relative to the ions of mass two, this function being:

where f(V) and F (V) are functions which take into account certain undesirable phenomena in the mass spectrometer.

In addition a direct measurement cannot be made for a given value of output voltage V since the latter primarily depends on the intensity of the beam comprising ions of mass two. Furthermore, in order to express a final result of measurement as accurately as possible, a re-calculated value R must be determined for R, according to a particular feature of the present invention, for a predetermined reference value of the output voltage V of the amplifier 33. In practice, this output voltage is between 20 and 30, so that it has been found convenient to adopt an output voltage V of 25 as the reference value.

The constants f(V and F(V are determined by calibrating the mass spectrometer according to the invention before it is used for analyses; this calibration leads to two linear curves which are indicated at 37 and 38 in FIGURE 4. These curves are obtained by plotting the concentration C of deuterium, in the liqiud and vapour phase respectively, in a plurality of mixtures of standardised waters and hydrogen sulphide, as ordinates, against the corresponding values of the ratio R, as abscissae, the axes of the graph having an arbitrary origin. The experimentally determined points on the curves 37 and 38 do not extend as far as the intersection point P, but they are graphically extrapolated to the point P. The ordinate of the point P represents the actual Zero concentration of deuterium as this point represents the condition of H 8 and H 0 in equilibrium having the same concentration of deuterium, which can only happen with zero concentration of deuterium.

The standardised waters are obtained by mixing light water and known quantities of substantially pure heavy water.

Following such calibration, the device according to the present invention is employed in the following way in order to obtain a quantitative determination of the deuterium content of the hydrogen-containing compound under investigation.

The ratio R is determined for different decreasing values of output voltage V of the amplifier 33, the said values being between 30 and 20 volts and being reduced by reducing the pressure in the expansion bulb 23 of the gas line by pumping out that part of the gas between the taps 22a and 22b. Each determination of the ratio R takes approximately five minutes and the results are then interpolated to obtain the reference value R of the ration R corresponding to the reference output voltage of 25 volts.

The device according to the invention is characterised by the possession of very appreciable advantages, more particularly the high degree of accuracy obtainable in circumstances in which such accuracy has hitherto appeared to be unattainable, other things being equal, and the relative rapidity with which such highly accurate results may be obtained.

In this connection, it may be mentioned that the field of use of a prototype constructed as above described with reference to FIGURES 1 and 2 extends from zero to 10 parts per million of deuterium in hydrogen, and that the degree of accuracy obtained is 0.2 ppm. for concentrations of the order of a hundredth of a p.p.m., and 0.1% for stronger concentrations.

We claim:

1. In an apparatus for isotopic separation by mass spectrography of hydrogen elements of hydrogen containing substances reduced prior to separation, a mass spectrograph, an ionisation chamber for said spectrograph, means for delivering a reduced hydrogen containing substance to said chamber comprising a gas line, a tubular extremity for said gas line, a leak in said extremity from said line leading to said chamber, a valve in said line, vacuum creating means connected to said valve, a second valve in said line, means for admitting hydrogen containing substances through said second valve to said line, a tubular member under low pressure connected to said extremity and to said chamber and means in said member for completely reducing the hydrogen containing substances including a reducing metal.

2. Apparatus as described in claim 1 in which said reducing metal is in solid state and has a large active surface area.

3. Apparatus as described in claim 1 in which said tubular member is U-shaped, heating means for said member, a capillary restriction between said member and said chamber, said reducing metal being uranium ribbon less than 0.4 mm. thick.

4. Apparatus as described in claim 1 in which said gas line includes an expansion chamber.

Nier Oct. 25, 1949 Huckabay Jan. 31, 1956 

1. IN AN APPARATUS FOR ISOTOPIC SEPARATION BY MASS SPECTROGRAPHY OF HYDROGEN ELEMENTS OF HYDROGEN CONTAINING SUBSTANCES REDUCED PRIOR TO SEPARATION, A MASS SPECTROGRAPH, AN IONISATION CHAMBER FOR SAID SPECTROGRAPH, MEANS FOR DELIVERING A REDUCED HYDROGEN CONTAINING SUBSTANCE TO SAID CHAMBER COMPRISING A GAS LINE, A TUBULAR EXTREMITY FOR SAID GAS LINE, A LEAK IN SAID EXTREMITY FROM SAID LINE LEADING TO SAID CHAMBER, A VALVE IN SAID LINE, VACUUM CREATING MEANS CONNECTED TO SAID VALVE, A SECOND VALVE IN SAID LINE, MEANS FOR ADMITTING HYDROGEN CONTAINING SUBSTANCES THROUGH SAID SECOND VALVE TO SAID LINE, A TUBULAR MEMBER UNDER LOWER PRESSURE CONNECTED TO SAID EXTREMITY AND TO SAID CHAMBER AND MEANS IN SAID MEMBER FOR COMPLETELY REDUCING THE HYDROGEN CONTAINING SUBSTANCES INCLUDING A REDUCING METAL. 